Hydraulic gain reduction circuit

Abstract

A gain reduction circuit is provided for use with a pressure flow compensated variable displacement pump in a power-on-demand hydraulic system. An orifice and a check valve are connected in parallel between a pressure-flow compensating valve and the control for the variable displacement pump. A second orifice is connected between the pump control and sump. A relief valve is connected in parallel with both orifices. The circuit operates to allow a quick increase in pump output, while damping variations in the pump control to prevent or minimize oscillation of the pump outlet pressure around the desired value. In alternative embodiments, the check valve may be omitted if larger orifices are used, or the check valve may be provided and the second orifice omitted.

I claim: 
     
       1. A gain control circuit for a variable hydraulic member having an inlet, an outlet and controlled by the pressure in a control line, the circuit comprising: demand valve means having a first position for connecting said control line to said inlet and a second position for connecting said control line to said outlet;   a load sense line the pressure in which is representative of a load demand on said hydraulic member, said demand valve means position being controlled by a difference between said load sense line pressure and the pressure at said outlet;   flow-limiting means for limiting flow rate therethrough and interconnecting said demand valve means and said control line;   uni-directional flow means connected in parallel with said flow limiting means for allowing flow therethrough from said control line towards said demand valve means and preventing flow from said demand valve means towards said control line; and   relief means for allowing flow therethrough towards said inlet from a demand valve means side of said flow-limiting and uni-directional flow means when the pressure at said side exceeds a pre-determined value.   
     
     
       2. The gain control circuit of claim 1, wherein said demand valve means is biased towards said first position. 
     
     
       3. The gain control circuit of claim 1, wherein said hydraulic member is selected from the group consisting of a valve and a variable displacement pump. 
     
     
       4. The gain control circuit of claim 3, wherein said hydraulic member comprises a variable displacement radial piston pump, the displacement of said pump increasing as the pressure in said control line decreases and decreasing as the pressure in said control line increases. 
     
     
       5. The gain control circuit of claim 1, wheren said unidirectional flow means comprises a check valve. 
     
     
       6. The gain control circuit of claim 1, wherein said flow-limiting means comprises an orifice. 
     
     
       7. The gain control circuit of claim 1, wherein said unidirectional flow means allows a typical flow therethrough approximately one order of magnitude greater than the typical flow allowed through either of said flow-limiting means and said relief means. 
     
     
       8. The gain control circuit of claim 7, wherein said flow-limiting means allows a flow therethrough of about 0.04 liters/second, said uni-directional flow means a flow of about 0.2 liters/second and said relief means a flow of about 0.03 liters/second. 
     
     
       9. The gain control circuit of claim 1, further comprising second flow-limiting means for limiting flow rate therethrough and interconnecting said control line and said inlet. 
     
     
       10. The gain control circuit of claim 9, wherein said first flow-limiting means is an orifice having a diameter of about 2.5 mm and said second flow-limiting means is an orifice having a diameter of about 1.5 mm. 
     
     
       11. A gain control circuit for a variable hydraulic member having an inlet, an outlet and controlled by the pressure in a control line, the circuit comprising: demand valve means having a first position for connecting said control line to said outlet and a second position for disconnecting said control line from said outlet;   a load sense line the pressure in which is representative of a load demand on said hydraulic member, said demand valve means position being determined by a difference between said load sense line pressure and the pressure at said outlet;   first flow-limiting means for limiting flow rate therethrough and interconnecting said demand valve means and said control line;   second flow-limiting means for limiting flow rate therethrough and interconnecting said control line and said inlet; and   relief means for allowing flow therethrough towards said inlet from a demand valve means side of said first flow-limiting means when the pressure at said side exceeds a pre-determined value.   
     
     
       12. The gain control circuit of claim 11 in said demand valve means is biased towards said second position. 
     
     
       13. The gain control circuit of claim 11, wherein said hydraulic member is selected from the group consisting of a valve and a variable displacement pump. 
     
     
       14. The gain control circuit of claim 13, wherein said hydraulic member comprises a variable displacement radial piston pump, the displacement of said pump increasing as the pressure in said control line decreases and decreasing as the pressure in said control line increases. 
     
     
       15. The gain control circuit of claim 11, wherein each said flow-limiting means comprises an orifice. 
     
     
       16. The gain control circuit of claim 15, wherein said first flow-limiting means has a diameter of about 3.0 mm, said second flow-limiting means has a diameter of about 2.5 mm and the maximum flow rate through said flow-limiting means is about 0.13 liters/second. 
     
     
       17. A gain control circuit for a pressure-on-demand variable displacement pump having an inlet and an outlet, the circuit comprising: a control line, the pressure in which regulates the displacement of the pump;   a demand valve having a first position connecting said control line to the pump inlet and a second position connecting said control line to the pump outlet, said demand valve being biased towards aid first position;   a load sense line the pressure in which is representative of a load demand on said pump, said demand valve position being controlled by a difference between said load sense line pressure and the pressure at said pump outlet;   a flow-limiting orifice interconnecting said demand valve and said control line;   a check valve connected in parallel with said orifice to allow flow therethrough from said control line towards said demand valve, but not from said demand valve towards said control line; and   a relief valve allowing flow towards said pump inlet from a demand valve side of said orifice and said check valve when the pressure at said side exceeds a pre-determined value.   
     
     
       18. The gain control circuit of claim 17, wherein said check valve allows a typical flow therethrough approximately one order of magnitude greater than the typical flow allowed through either of said orifice and said relief valve. 
     
     
       19. The gain control circuit of claim 17, further comprising a second flow-limiting orifice interconnecting said control line and said pump inlet.